Extremum Seeking Method for Optimal Voltage Regulation using Volt-Var and Volt-Watt Curves

This paper proposes a method for optimal voltage regulation in a distribution grid by coordinating active and reactive power of inverter-based resources at the point of connection (POC). This enables each smart inverter to provide grid support functionality of voltage regulation optimally. The objective is realized by simultaneously enabling Volt-Var and Volt-Watt functions and online adjusting active and reactive power settings according to the R/X ratio of the Thevenin impedance seen by a smart inverter. The proposed online adjustment is carried out using extremum seeking control which directs smart inverter to inject optimum combination of active and reactive power at POC. The proposed method considers recommendations of IEEE 1547 standard for voltage regulation and enables each DER to provide extra value by offering voltage regulation service while exchanging active power to the grid along with the reactive power. The proposed method also increases observability in the distribution grid as it keeps track of the R/X ratio at each inverter connected node. The robustness of this technique under rapidly changing impedance is also shown.